Method and arrangement for positioning a shoe of a shoe press/shoe calendar in a paper machine

ABSTRACT

The invention relates to a method for positioning a shoe of a shoe press/shoe clender in a paper machine. In the method, the position of the shoe ( 11 ) of the shoe calender/shoe press is measured and, based on the results of the measurement, the position of the shoe is controlled so as to be as desired in the direction of nip compression. The invention also relates to an arrangment for positioning a shoe of a shoe press/shoe calender in a paper machine, which arrangment comprises a shoe roll ( 10 ) or equivalent which includes a shoe ( 11 ) and hydraulic cylinders ( 12 ) connected thereto for moving the shoe ( 11 ). The arrangement comprises further at least two measuring devices ( 15 ) for measuring the position of the shoe ( 11 ) and means ( 12 ) for controlling the position of the shoe ( 11 ) based the results obtained by means of the measuring devices so as to be as desired in the direction of nip compression.

The invention relates to a method for positioning a shoe press/shoecalender in a paper machine.

The invention also relates to an arrangement for positioning a shoe of ashoe press/shoe calender in a paper machine, which arrangement comprisesa shoe roll or equivalent which includes a shoe and hydraulic cylindersconnected thereto for moving the shoe, and a support element to whichthe hydraulic cylinders and the shoe are attached.

As known in the state of the art, as loading rolls in a shoe press/shoecalender are used loading rolls in which a shoe is placed inside apolyurethane belt. The belt is attached at ends so as to be oilproof andthe sock/belt is held tight around the shoe structure. The shoestructure comprises oil ducts and hydraulic cylinders for pressing theshoe against a backing roll/thermoroll. One known arrangement for aso-called belt calender is disclosed in FI patent application 943278,which discloses a device for polishing a paper web or a board webprovided with a polishing zone through which the web is passed and whichhas a given thickness measured in the direction of the web to achieve alonger time of dwell of the web. The device is provided with twopolishing surfaces defining the polishing zone on both sides, one ofsaid surfaces being formed by a mantle of a machine-driven roll and theother of said surfaces being formed by a glide felt that runs around;provided with a glide shoe which is wrapped by the glide felt and whichhas a glide surface complementary to the mantle surface of the roll;provided with means for pressing the roll and the glide shoe againsteach other.

One problem in the known arrangements is that the position of the shoeis not known, wherefore, for example, when closing, the shoe may bepositioned unevenly with the result that an uneven nip force isproduced. This may lead, among other things, to breaking of the web.

One problem in calenders, at high speeds in particular, because of anundesirable position of the shoe, is an uneven/undesirable type of drawwhich is effective in the nip, in which connection uneven compressionmay break the web.

Moreover, a problem in presses under heavy load is that when the shoe isin an undesirable position, the backing roll and the belt will wear. Inaddition, problems may arise in the lubrication of the shoe because,when the shoe is out of line, a lubricating oil film is thinner on theedge which comes first into contact with the backing roll.

In a press section, problems may be caused by the fact that, when thenip is closed in an undesirable manner, the press felt may be crumpled.

In high-speed machines with a speed of over 1000 m/min, problems mayarise in the controllability of felts and wires, if the shoe pullsfelts/wires askew because of its incorrect position.

An object of the invention is to create a solution to the problemsdescribed above.

An object of the invention is to create an arrangement in which theposition of the shoe is known and the shoe can be guided to a desiredposition, whereby the problems described above are eliminated.

With a view to achieving the objectives described above as well as thosewhich will come out later, the method according to the invention ismainly characterized in that, in the method, the position of a shoe of ashoe calender/shoe press is measured and that, in the method, theposition of the shoe is controlled based on the results of themeasurement so as to be as desired in the direction of nip compression.

The arrangement according to the invention is in turn mainlycharacterized in that the arrangement comprises further at least twomeasuring devices for measuring the position of the shoe and means forguiding the shoe as desired in the direction of nip compression based onthe results obtained by means of the measuring devices. In accordancewith the invention, the means for controlling the shoe based on theresults obtained by the measuring devices include a processing unit,which can be, for example, a programmable logic or a process orcomputing station (CPU) of a distributed automation system. The signalscomputed by the processing unit can be passed to valves which controlthe movement of cylinders controlling the movement of the shoe, forexample, by using standard current or voltage signals of instrumentationor some automation field bus.

In accordance with the invention, the position of the shoe in a shoecalender/shoe press is measured by at least two measuring devicessuitable for position measurement, for example, a linear sensor. Theposition measuring sensors are placed most advantageously close to theedges of the driving and tending sides and in wide machines also in themiddle area. In that connection, the position of the shoe is found out,and the nip is caused to close in a desired position since the movementsof the hydraulic cylinders can be regulated accurately based on themeasurement results obtained.

In accordance with the invention, the shoe of the shoe press/shoecalender is provided with at least two position measuring sensors andthe movement of the shoe is regulated based on data provided by thesensors, for example, utilizing a computing algorithm, and the hydrauliccylinders are controlled to operate such that a desired movement andposition of the shoe is assured in the direction of nip compression.

When the nip is closed/opened in accordance with the invention, there isno risk of the web breaking, because the position of the shoe is knownprecisely when the measurement result provided by the position measuringsensors has been received, and the shoe can be positioned in a desiredposition. In accordance with the invention, also after a web break ordowntime, it is possible to control the oil flows of the hydrauliccylinder based on the position data obtained from the position measuringsensors such that the nip is controlled to close in a desired manner,whereby the position of the shoe is caused to be as desired.

In the arrangement according to the invention, the shoe can thus becontrolled to close in an optimal manner with respect to the runningsituation.

In the following, the invention will be described in more detail withreference to the figures in the accompanying drawing, to the details ofwhich the invention is, however, not by any means intended to benarrowly confined.

FIG. 1 schematically shows a shoe roll with which one application of thearrangement according to the invention has been combined.

FIG. 2 schematically shows one application of the measurementarrangement according to the invention.

FIG. 3 shows loading of a shoe roll in the direction of nip compressionas a schematic application.

As shown in FIGS. 1 and 2, an extended-nip roll, or a shoe roll 10comprises a shoe 11 located inside a belt 13, which shoe includeshydraulic cylinders 12 for loading the shoe 11. In a loading situation,the belt 13 adjusts itself to the shape of the nip between the shoe roll10 and a backing roll, to the shape of the shoe 11. The hydrauliccylinders 12 and the shoe 11 are fixed to a frame 14 of the roll 10 andat least two position measuring sensors 15 are arranged in connectionwith the shoe 11 between the shoe 11 and the frame 14 inside theextended-nip (shoe) roll 10, the position of the shoe 11 between theextended-nip roll 10 and the backing roll 20 in the nip being controlledso as to be of a desired shape based on data provided by the positionmeasuring sensors. Of course, the shoe structure also includes thenecessary oil ducts and structures associated therewith, which are notshown in the figures for the sake of clarity. The measuring apparatus orarrangement can be, for example, a linear sensor or an absolute sensor.In order to identify the position of the shoe it is also possible to usesome optical arrangement which could be, for example, a directionallight source attached to the shoe and moving with the shoe, and a CCDcamera matrix fixedly mounted on the frame. In that connection, thelocation of the shoe would become clear from which of the CCD cells“see” a light signal.

The arrangement shown in FIG. 1 comprises three position measuringsensors 15, the regulation of the position of the shoe 11 beingperformed based on position measurements 16 ₁, 16 ₂, 16 _(N) (FIG. 2)provided by said sensors by computing signals 18 ₁, 18 ₂, . . . 18 _(N)in a processing unit 17 based on a computing algorithm, which signalsare flow instructions for hydraulic valves 19. The movement of thehydraulic cylinders 12 is controlled by means of the signals 18 ₁, 18 ₂,. . . 18 _(N) in order to move the shoe 11 in a desired manner to adesired position in the direction S of nip compression (FIG. 3).

The arrangement in accordance with the invention comprises at least twomeasuring devices 15 for measuring the position of the shoe 11 and means12; 16 ₁, 16 ₂, 16 _(N); 17; 18 ₁, 18 ₂, . . . 18 _(N); 19 forcontrolling the position of the shoe 11 based on the results obtainedfrom the measuring devices so as to be as desired.

In accordance with an embodiment of the invention regarded asadvantageous, the position of the shoe roll 10 of a press/calender ismeasured by means of the position measuring sensors 15, and when theposition of the shoe 11 of the shoe roll 10 is found to be incorrectbased on the measurement results 16 ₁, 16 ₂, 16 _(N), the means forrectifying the position of the shoe 11 are activated. The regulation ofthe position of the shoe 11 is carried out based on a computingalgorithm by computing in the processing unit 17 the control signals 18₁, 18 ₂, . . . 18 _(N) for the hydraulic cylinders 19. The computingalgorithm may be, for example, of the form ΔQ=f (ΔX), whereinQ=Q₀-Q_(N), i.e. a change in the flow of oil, and X=X_(T)-X_(M), i.e. adesired shoe position—a position measurement. The regulation of positioncontrols the hydraulic valves 19 such that the hydraulic cylinders 12change the position of the shoe 11 to a desired position in which theshoe 11 can be askew or straight. Normally, the desired position of theshoe 11 is “straight”, which means that all the measuring devices 15 getsubstantially the same value as a result of the measurement of theposition. The results must, of course, be interpreted within the limitsof the measurement accuracy of the devices.

Example: if there are 2 sensors in use and their measurement accuracy is±1 mm. Then the measurement result

sensor 1: x₁ = 12.31 mm sensor 2: x₂ = 12.14 mm x_(d) = x₁ − x₂ = 0.17mm measurement accuracy of sensors: e_(x) = 0.1 mm

can be interpreted as a situation “shoe straight” because the deviationx_(d) is not significantly greater than the measurement accuracy e_(x).

However, if it were desired for some reason or other that the positionof the shoe be askew instead of straight (for example, on the tendingside 3 mm higher than on the driving side), the arrangement according tothe invention also allows that.

The invention may also be applied when the nip is closed/opened betweenthe shoe roll 10 and its backing roll thermoroll such that the shoe 11opens/closes in an optimal fashion, for example, in a desired positionand/or at a desired speed. When there is available analog measurementdata on the position of the shoe 11 according to the invention, the nipcan be controlled so as to close also in a manner other than at auniform speed. It is possible that at the initial stage of closing, whenthe nip is still clearly open, it is beneficial to carry out themovement as quickly as possible. When the nip starts to be almostclosed, it is advisable to slow down the movement in order that theclosing operation should take place more softly. Different paper gradesmay require that the closing of the nip is softened differently—in thecase of thick and durable paper grades the function is not needed atall, whereas in the case of grades which are thin or otherwise poorer instrength, the slowing down of the closing at the final stage isnecessary.

As shown in FIG. 3, the shoe 11 of the extended-nip roll 10 is guided toa desired position in the direction of nip compression S so as to beloaded against the backing roll 20. The cross-machine direction isdenoted in the figure with the reference sign W.

Above, the invention has been described only with reference to some ofits advantageous embodiment examples, to the details of which theinvention is, however, not intended by any means to be narrowlyconfined. Many variations and modifications are feasible within theinventive idea defined in the accompanying claims.

What is claimed is:
 1. A method for closing a shoe, positioned within abelt, against a backing roll to form a nip between the backing roll, thebelt and the shoe of a shoe press/shoe calender in a paper machine, thenip extending in a cross machine direction, the method comprising thesteps of: measuring the position of the shoe within the belt of the shoecalender/shoe press with respect to a reference position at at least twopositions which are spaced from each other in the cross machinedirection; and closing the shoe within the belt against the backing rollwhile controlling the position of the shoe based on the results of themeasurement so the nip is of a desired shape.
 2. The method of claim 1wherein the position of the shoe with respect to the reference positionis measured by at least two position measuring sensors.
 3. The method ofclaim 2 wherein the shoe has a driving side edge and a tending sideedge, and wherein the position of the shoe is measured by a positionmeasuring sensor close to the driving side edge, and a position sensorclose to the tending side edge.
 4. The method of claim 3 wherein aposition sensor is also located in the middle of the machine, and theposition of the shoe is measured by the position measuring sensor closeto the driving side edge, the position measuring sensor close to thetending side edge, and the position sensor located in the middle of themachine.
 5. The method of claim 1 wherein the movement of the shoe isregulated based on the measurement results utilizing a computingalgorithm, and hydraulic cylinders of the shoe of the shoe press/shoecalender are controlled to operate such that he shoe moves in a desiredmanner to a desired position.
 6. The method of claim 1 wherein the stepof closing the shoe against the backing roll includes quickly closingthe nip when in the initial stages of closing, and slowing down themovement when the nip starts to be almost closed.
 7. The method of claim6 wherein the backing roll is a thermoroll.
 8. The method of claim 1wherein the reference position is a fixed position on a frame to whichthe shoe is mounted.
 9. An arrangement for closing a shoe within a belt,against a backing roll to form a nip between the backing roll and theshoe of a shoe press/shoe calender in a paper machine, the nip extendingin a cross machine direction, the arrangement comprising: a shoe roll,having a shoe, a belt within which the shoe is positioned, and hydrauliccylinders connected to the shoe for moving the shoe towards and awayfrom the backing roll; at least two measuring devices for measuring theposition of the shoe, the measuring devices being positioned todetermine the position of the shoe with respect to a reference positionat two positions on the shoe which are spaced in the cross machinedirection; and means for controlling the position of the, shoe duringthe closing of the shoe against the backing roll to form the nip basedon the results obtained by the measuring devices so the nip is of adesired shape.
 10. The arrangement of claim 9 wherein the at least twomeasuring devices comprise position measuring sensors placed close to atending side edge of the paper machine and a driving side edge of thepaper machine.
 11. The arrangment of claim 10 further comprising aposition measuring sensor placed in the middle of the paper machinebetween the tending side edge and the driving side edge.
 12. Thearrangement of claim 9 further comprising means for moving the hydrauliccylinders based on the results of the measurement in order to positionthe shoe in a desired position.
 13. The arrangement of claim 9 furthercomprising a unit in which a computing algorithm is called out based onthe results of the measurement in order to give flow instructions tohydraulic valves which control the hydraulic cylinders such that thehydraulic cylinder move the shoe to a desired position.
 14. An apparatusfor closing a shoe against a backing roll to form a nip between thebacking roll and the shoe in a paper machine, the apparatus comprising:a backing roll; a shoe; a belt within which the shoe is positioned, theshoe being loaded against the backing roll to define a nip by aplurality of hydraulic cylinders; a frame extending within the belt, thehydraulic cylinders supporting the shoe on the frame; at least twoposition measuring sensor arranged in connection with the shoe betweenthe shoe and the frame, the sensors measuring the position of the shoeand producing position measurements, the position measuring sensorsbeing spaced from one another in a cross machine direction; and aprocessing unit which receives the position measurements from theposition measuring sensors, the processing unit generating signals whichcontrol the hydraulic cylinders to close the shoe towards the backingroll.
 15. The apparatus of claim 14 wherein the at least two positionmeasuring sensors comprise: a position measuring sensor placed close toa tending side edge of the paper machine; a position measuring sensorplaced close to a driving side edge of the paper machine; and a positionmeasuring sensor placed in the middle of the paper machine.